A reach stacker is a vehicle used for handling intermodal cargo containers (ISO containers) in small and medium-sized ports. Reach stackers are able to transport a container short distances very quickly and stack them. Reach stackers are widely used for container stacking because of their flexibility, higher stacking and lifting and container handling capacity when compared to forklift trucks. Using reach stackers, container blocks can have a depth of 4 to 6 row of containers, due to second/third row access. Furthermore, containers can be stacked typically up to 5 containers high.
When a container on the top of a row has to be manipulated, the operator has to maneuver the reach stacker in front of the container block, extend the boom and position the spreader over the container surface. Finally, the twistlock mechanisms on the spreader have to be positioned above the matching holes in the corners of the container and subsequently moved and locked into the holes.
FIG. 1 depicts one embodiment of a container 10 with twistlock holes 12. FIG. 2A depicts a twistlock 14 in an unlocked position, but not engaged with a twistlock hole 12, and FIG. 2B depicts the twist lock 14 in a locked position, but also not engaged with a twistlock hole 12.
It can be appreciated from FIGS. 2A and 2B, that the twistlock 14 has an upper portion 16 and a lower portion 18. The lower portion 18 is fixed, while the upper portion 16 can be selectively rotated. In the unlocked position, the upper portion 16 is aligned with the lower portion 18. In the locked position, the upper portion 16 is turned with respect to the lower portion 18, so that the upper portion 16 extends over and beyond the lower portion 18. The upper portion 16 may be turned approximately 90 degrees with respect to the lower portion 18 so that the upper portion 16 extends beyond the perimeter of the lower portion 18.
The twistlock 14 is dimensioned to fit into the twistlock hole 12. Once in the hole 12, the upper portion 16 is rotated. The rotated upper portion 16 engages with the material surrounding the hole 12 to lock the upper portion 16 to the container 10.
The operator has to perform the entire operation from ground level while the container 10 is positioned at heights in excess of 15 m. Typically the operator has no feedback during the operation, however, the operator does get a confirmation once the twistlock 14 is engaged. It can therefore be appreciated that the time to locate the twistlock 14 into the hole 12 largely depends on operator experience. Even experienced, trained operators can take a considerable amount of time to locate the twistlock 14 into a container hole 12.
While the above discussion is focused on reach stackers, twistlocks 14 are not limited to reach stackers. Instead, several other kinds of vehicles, such as empty-container handlers, container stackers and material handling equipment, such as gantry cranes, use twistlocks. The solution proposed herein to the current disadvantageous method of using twistlocks applies to these applications as well.
Several companies in the market offer systems that help operators in the locking operation. One of such commercial systems is called View-on-twistlocks' by Orlaco. The View-on-twistlocks system consists of cameras fitted on either side of the spreader and aimed at the twistlocks. Each camera displays its images on its own monitor.
This system has some major drawbacks that include, but are not limited to, the need to use multiple high resolution cameras, each camera needs its own display, or one display capable of combining all of the camera images, the cameras and displays are expensive, the operation is entirely performed by the operator, and the operator must focus all of his attention on the screen(s), which can lead to accidents because the driver can't also pay attention to his surroundings.
An automatic method to detect the twistlock holes, move the spreader twistlocks towards these holes and achieve the locking is thus desirable. Fully autonomous locking is however not necessary in most cases, as the operator needs to stay in control for safety reasons and to obtain a smooth handling sequence of the total operation.
To solve the problem associated with the prior art three steps may be used. First, the location of the twistlock hole position is detected. Second, a method of control to guide the twistlocks to the hole position is needed. Lastly, an actuation mechanism incorporating the necessary sensor input, operator input, control algorithm, and actuator signal is needed.